Exercise treadmills are well known. Typically exercise treadmills will either be powered or unpowered. Powered treadmills typically have a drive roller and a free roller separated by a deck. A flexible endless belt is provided, under tension, to allow the endless belt to ride across the deck. The user walks along the outer surface of the flexible belt between the drive roller and the free roller. The deck provides support for the walking surface of the belt. Typically, the treadmill is inclined and frequently the speed of the belt may be controlled by an electronic unit which controls an electric motor.
Exercise treadmills, especially those found in institutions and health clubs undergo a lot of use and must be sturdily built. Cheaply-constructed or poorly-designed treadmills have failed in a number of areas. A particular problem area, even with well designed and well constructed treadmills, is the wear on the belt.
As the treadmill is used, the belt tends to relax and stretch. This often occurs along the outside edges and is visible when fraying occurs in this area. A stretched, worn belt will tend to wander side-to-side across the rollers. This disrupts the user and will aggravate the belt wear problem. Typically, treadmills are provided with an inch or two of exposed rollers which extend beyond the edges the endless belt. This will allow some room for the belt to wander, but is undesirable as it decreases the walking area provided for the user. It would be advantageous if treadmills could utilize the full width of the rollers by eliminating the wandering belt problem.
The problem of belt misalignment which causes the belt to develop a tendency to wander from one side to the other when in use--has been addressed in a number of ways. Some designs use crowned rollers which have a thicker central section which tapers out to either end. While these reduce the tendency of the belt to wander from side-to-side, they are expensive to machine. In U.S. Pat. No. 3,554,451, an endless belt is disclosed which has an alignment ridge coincident with the lateral axis of the belt which mates with an annular groove in the center of the rollers. In this system, the ridged center of the belt produces a slightly convex walking surface.
The exercise treadmill of the present invention provides for annular grooves in the drive and free rollers which grooves are located, not in the center of the rollers but to one or both sides of the center. A linear groove in the deck surface aligned with the grooves in the rollers allows a flexible belt with an alignment ridge on the underside to be used, which helps prevent the belt-wandering problem. This system provides the advantage of allowing the manufacture to use a smaller wall tubing. That is, an annular groove to one or both sides of the longitudinal axis of the belt will be less likely than a groove in the center to cause sudden roller failure or cracking at the groove.
Applicant's present invention provides for hollow cylindrical rollers mounted by bearings to axle shafts. The axles are mounted generally perpendicular to the side rails of the treadmill. The rollers have outside walls having annular grooves and alignment ridges on the underside of the endless belt, which groove/ridge is located to one side of the rollers rather than the central area, decreasing the likelihood of failure in the roller during use of the treadmill. That is, the belts are mounted between the rollers under tension which is borne by the surface of the drive and free rollers. Applicant has found a reduced likelihood of shaft failure by mounting the shaft with an annular alignment groove off of the center. The use of a single groove (asymmetrical design) has not resulted in a significant tendency of the belt to skew to one side. To the extent that such a tendency exists, it may be "adjusted out" by adjustment screws in the free roller that allow adjusting the roller in a slightly out-of-perpendicular arrangement. Such adjustment mechanisms are old in the art, having been used to address belt and machine adjustment with prior art belts.
Applicant has found that the use of a single set of grooves (two roller grooves and a deck groove) to one side of the longitudinal axis of the treadmill, rather than one set on each side or the symmetrical groove arrangements found in the prior art, to have some advantages. First, it is more difficult with a groove set on each side of the roller to maintain the same distance between the pair of alignment ridges on the belt, which often stretches with use. Once this occurs, one ridge will try to ride out its groove, aggravating rather than maintaining proper alignment. Second, it is more expensive to have more than one set of grooves. Nonetheless, Applicants' novel invention may be practiced with annular grooves on both sides.